A battery is mainly divided into a primary battery and a secondary battery. Here, the primary battery may not be reused after once being used since it uses an irreversible reaction to generate electricity, for example, a dry cell, a mercury battery, a Volta battery, or the like, that are generally used. On the contrary, the secondary battery may be reused by being charged after being used since it uses a reversible reaction, for example, a lead acid battery, a lithium ion battery, a Ni—Cd battery, or the like.
A lithium ion battery, which is one of the secondary batteries, is configured to include a negative electrode generally made of carbon, a positive electrode generally made of a lithium compound, an electrolyte positioned between the two electrodes, and an electric wire connecting the negative electrode and positive electrode to each other. Lithium ions in the electrolyte move to the negative electrode at the time of charging and move to the positive electrode at the time of discharging, and excess electrons are discharged or absorbed in each electrode, thereby causing a chemical reaction. The electron flows in the electric wire in this process, and as a result, electric energy is generated. Although the case of the lithium ion battery is described by way of example here, in the case of other secondary batteries, the basic principle and structure are the same as those of the lithium ion battery except that materials used as the electrode or the electrolyte are changed. That is, in general, the secondary battery is configured to include the negative electrode, the positive electrode, the electrolyte, and the electric wire as described above.
In this case, the secondary battery may be configured to include one negative electrode, one positive electrode, one electrode, and one electric wire, but more generally, may be formed by connecting a plurality of unit cells configured of one negative electrode, one positive electrode, one electrode, and one electric wire to each other. That is, the plurality of unit cells as described above are filled in the secondary battery pack. The unit cells are electrically connected to each other, respectively.
Generally, the secondary battery includes the plurality of unit cells and has a shape in which a pair of external terminal taps connected to electrodes of each of the cells (that is, a tap configured of a pair of a negative electrode connected to the negative electrode of each of the unit cells and a positive electrode connected to the positive electrode of each of the unit cells per one battery to serve as an electrode) is exposed to the outside. In the secondary batteries as described above, generally, a plurality of positive electrodes and negative electrodes are connected to each other to form a battery as a single pack rather than using a single positive electrode and a single negative electrode.
As a positive electrode active material for a lithium secondary battery, a lithium active material precursor such as Li-M-P based (M is at least one selected from a group consisting of Fe, Mn, Co, and Ni), Li—Mn—Ni based, Li—Ni—Mn—Co based materials has been used as disclosed in Korean Patent Laid-Open Publication Nos. 2009-0020288 and 2009-0006898.
However, a LiNi1/3Co1/3Mn1/3O2 material widely used as the positive electrode active material for a lithium secondary battery has a capacity of about 150 mAh/g at the time of testing the capacity using a half cell in the case in which a cut-off voltage is 3.0 to 4.3V. Therefore, in order to manufacture a high capacity battery such as a battery for an electric vehicle (EV), the development of a high capacity positive electrode active material has been urgently demanded.